Benniston L5

Question 1

Order ligands is order from strongest to weakest trans effect

Answer 1

strongest
1) CO, CN-, C2H4 (ethene)
2) PR3, H-
3) Me-
4) Ph-, NO2-, I-
5) Br-, Cl-
6) py, NH3, OH-, H2O

Question 2

How can we explain the trans effect list

Answer 2

We must think about what happens when the complex goes from the ground state to the transition state.
An increase in reaction rate can be viewed as a decrease in the activation barrier.

Question 3

How can we decrease the activation barrier

Answer 3

we can do this in two ways
- destabilisation of the ground state (thermodynamically trans effect)
- stabilisation of the transition state (kinetic trans effect)

Question 4

What are the two cases when looking at the thermodynamic trans effect

Answer 4

Can Look at this in terms of sigma donors or pi acceptors

Question 5

Describe the thermodynamic trans effect with sigma-donors

Answer 5

metal σ-orbital is empty and so ligands (T and X) donate electron density. If T is the stronger σ donor then the M-X bond is weaker, destabilisation effect

Question 6

Describe the thermodynamic trans effect with pi acceptors

Answer 6

pi orbital of metal is filled and donates electron density into empty orbital on the ligands (T and X). Pi back donation strengthens the bond, so if T is the better acceptor then the M-X bond is weakened

Question 7

Describe the kinetic trans effect

Answer 7

assumed to operate because of better bonding between ligand (T) and M in the transition state. T can improve its bonding to M if it is a good σ donor or pi acceptor which offsets loss of bonding to x

Question 8

What are the two different types of electron transfer reactions

Answer 8

Two basic mechanisms occur
- inner sphere
- outer sphere

Question 9

describe electrons transfers reactions

Answer 9

one species is the oxidant (must be reduced) the other species is the reductant (must be oxidised)

Question 10

What factor effect electron transfer

Answer 10

1) distance
2) thermodynamic favorability
3) changes in bond lengths of oxidant and reductant
4) spin change restrictions

Question 11

How does distance effect electron transfer

Answer 11

the distance in which an electron can hop is important as solvent or ligands can insulate the two reacting species

Question 12

How do we determine if an electron transfer is thermodynamically favourable

Answer 12

∆G0 = -nF∆E Can be determined by the relative redox potentials of the two species.
If G is negative the reaction is spontaneous electron transfer is favourable
If G is positive the reaction is not spontaneous and the electron transfer is not favourable